Merge pull request #471 from SuryaChaitanya1998/py1

Added quicksot in python 3

Author: t2013anurag

sorting/quick_sort/quicksort.py

@@ -1,37 +1,30 @@
-def partition(myList, start, end):
-    pivot = myList[start]
-    left = start+1
-    # Start outside the area to be partitioned
-    right = end
-    done = False
-    while not done:
-        while left <= right and myList[left] <= pivot:
-            left = left + 1
-        while myList[right] >= pivot and right >=left:
-            right = right -1
-        if right < left:
-            done= True
-        else:
-            # swap places
-            temp=myList[left]
-            myList[left]=myList[right]
-            myList[right]=temp
-    # swap start with myList[right]
-    temp=myList[start]
-    myList[start]=myList[right]
-    myList[right]=temp
-    return right
-
-def quicksort(myList, start, end):
-    if start < end:
-        # partition the list
-        split = partition(myList, start, end)
-        # sort both halves
-        quicksort(myList, start, split-1)
-        quicksort(myList, split+1, end)
-    return myList
-
-def main():
-    myList = [7,2,5,1,29,6,4,19,11]
-    sortedList = quicksort(myList,0,len(myList)-1)
-    print(sortedList)
+from random import randrange
+
+
+def partition(lst, start, end, pivot):
+    lst[pivot], lst[end] = lst[end], lst[pivot]
+    store_index = start
+    for i in xrange(start, end):
+        if lst[i] < lst[end]:
+            lst[i], lst[store_index] = lst[store_index], lst[i]
+            store_index += 1
+    lst[store_index], lst[end] = lst[end], lst[store_index]
+    return store_index
+
+
+def quick_sort(lst, start, end):
+    if start >= end:
+        return lst
+    pivot = randrange(start, end + 1)
+    new_pivot = partition(lst, start, end, pivot)
+    quick_sort(lst, start, new_pivot - 1)
+    quick_sort(lst, new_pivot + 1, end)
+
+
+def sort(lst):
+    quick_sort(lst, 0, len(lst) - 1)
+    return lst
+
+print sort([])
+print sort([1, 2, 3, 4])
+print sort([-5, 3, -2, 3, 19, 5])